func wordBreak(s string, wordDict []string) bool {
	// 先把wordDict放在字典中
	word := make(map[string]bool)
	for _, w:= range wordDict {
		word[w] = true
	}
	dp := make([]bool, len(s) + 1)
	dp[0] = true
	for i:= 0; i< len(s); i++ {
		for j := 0; j <i ; j++ {
			if dp[j] && word[s[j:i]] {
				dp[i] = true
				break
			}
		}
	}
}
